ANALYTICAL CHEMISTRY. Introduction to Titration

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1 ANALYTICAL CHEMISTRY by Wan Norfazilah Wan Ismail Faculty of Industrial Sciences & Technology

Chapter Description Expected Outcomes Describe the principles of equilibria involved in chemical analysis particularly gravimetry and volumetry.

2 Chapter Description Expected Outcomes Describe the principles of equilibria involved in chemical analysis particularly gravimetry and volumetry. Understand and apply the equilibrium constant based on concentration of species (Kc) to predict how far a reaction will proceed. State the factors that affect equilibrium and the Le Chateliar s principle. Understand and apply the concept of titration.

3 Contents Equilibrium Le Chateliar s Principles Introduction to titration Types of Titrimetry Titrant and Titrand Volumetric Calculations

4 EQUILIBRIUM aa + bb cc + dd reactants products At equilibrium: forward rate of reaction = reverse rate of reaction K = C c D d A a B b K = A a B b C c D d = 1 K A, B, C, D cccccccc sssssss a, b, c, d ssssssssssss cccccccccccc K eeeeeeeeeee cccccccc ccccccccccccc oo A, B, C aaa D

EQUILIBRIUM IN AQUEOUS SOLUTION & GASEOUS STATE N 2 O 4 g 2NN 2 g K c = NN 2 2 N 2 O 4 ** An equilibrium that involves pressure, concentration is equivalent to the partial pressure or (mol ratio P

5 EQUILIBRIUM IN AQUEOUS SOLUTION & GASEOUS STATE N 2 O 4 g 2NN 2 g K c = NN 2 2 N 2 O 4 ** An equilibrium that involves pressure, concentration is equivalent to the partial pressure or (mol ratio P total ). P = nnn V = CCC Ideal gas law K P = P NN2 2 P N2 O 4 C = mmmmm ccccccccccccc P = pppppppp ** Concentration of pure solid or pure liquid is constant. Therefore: K P = K C C = mmmmm ccccccccccccc P = ppppppp pppppppp

6 HETEROGENEOUS EQUILIBRIUM ** Heterogeneous equilibrium occurs when the species in equilibrium exist in different phase. CaaO 3 s CCC s + CC 2 g K = CC 2

7 LE CHATELIAR S PRINCIPLE When a change is applied to disturb a system at equilibrium, the reaction will favor to reduce the effect of the change. Factors that affect equilibrium systems are: Temperature Pressure or volume Concentration of the reactant or product

8 EFFECT OF CONCENTRATION N 2 g + 3H 2 (g) 2NN 3 g K = NN 3 2 N 2 H 2 3 ** To find the effect of change in concentration, use reaction quotient, Q. Q = NN 3 o 2 N 2 o H 2 o 3 "o" = oooooooo ccccccccccccc Q = K c : system will be in equilibrium Q > K c : system will shift to the left Q < K c : system will shift to the right until Q = K c is achieved

9 EFFECT OF TEMPERATURE For endothermic reactions the K c value increases For exothermic reactions the K c value decreases EFFECT OF TEMPERATURE A catalyst does not change the direction of reaction of K c value A catalyst changes only the rate of reaction, not the equilibrium position

10 INTRODUCTION TO TITRATION Definition: Titration = a method to determine the quantity of a reagent (known concentration) required to react with a known volume of sample (unknown concentration).

11 TYPES OF TITRIMETRY Volumetric titrimetry involves calculating the amount of a sample by a known volume of standard solution until the end point. Gravimetric titrimetry the mass of a product is used to calculate the quantity of the original analyte Coulometric titrimetry the concentration of a species is measured using a constant direct electrical current that consumes the analyte

12 TYPES OF VOLUMETRIC TITRATION Volumetric titration can be divided into: i. Acid-base or neutralization ii. iii. iv. Precipitation Complex formation Oxidation-reduction (redox)

13 TERMS USED IN TITRIMETRY Standard solution: a reagent of known concentration used to carry out a titrimetric analysis Equivalence point: a point in a titration when the mole of titrant is equivalent to the mole of analyte Back titration : a technique where the excess of a reagent used to neutralize the sample is determined by a titration with a second reagent

14 TERMS USED IN TITRIMETRY End point: the point where the titration is terminated which is determined by changes of indicator. Titration error: the difference between the equivalence point and the end point V ep = actual volume of reagent V eq = theoretical volume to reach the equivalence point E t = V ep V eq

15 TERMS USED IN TITRIMETRY Indicator: reagent added to the analyte solution to produce an observable physical change (the end point) at or near the equivalence point Primary standard: ultrapure compound that is used to determine the concentration of the standard solution in volumetric & mass titrimetric methods Secondary standard: less pure compound whose composition is reliably known and serves as reference material for a titrimetric method of analysis

16 REQUIREMENTS FOR PRIMARY STANDARD Highest purity Good stability High solubility High formula weight Easily available at reasonable cost Free from hydrated water and unable to absorb moisture

17 DESIRABLE PROPERTIES OF STANDARD SOLUTIONS Stable React rapidly and completely with the analyte Undergo a selective reaction with the analyte

18 APPARATUS OF VOLUMETRIC TITRIMETRY

19 MEASURING THE VOLUME IN THE BURETTE ml

20 TITRATION METHOD

21 TITRANT & TITRAND In titrimetry we add a reagent, called the titrant, to a solution containing another reagent, called the titrand, and allow them to react. In acid base titrations, an acidic or basic titrant reacts with a titrand that is a base or an acid Complexometric titrations: metal ligand complexation Redox titrations: titrant is an oxidizing or reducing agent Precipitation titrations: titrand and titrant form a precipitate.

22 VOLUMETRIC CALCULATIONS amount A (mol) = amount A (mmol) = amount A (mol) = volume (L) mass A (g) molar mass A (g / mol) amount A (mmol) = volume (ml) mass A (g) millimolar mass A (g / mmol) concentration A concentration A mol L mmol ml

23 VOLUMETRIC CALCULATIONS Calculate the molarity of standard solutions Refer to Chapter 2 Treating titration data Example: A 50.00mL portion of HCl solution required 29.71mL of M Ba(OH) 2 to reach an end point with bromocresol green indicator. Calculate the molarity of the HCl. (Ba: g/mol, Cl: 35.5 g/mol) Ba(OH) 2 + 2HCl BaCl 2 + 2H 2 O by Wan Norfazilah Ans: HCl Wan Ismail = M

24 VOLUMETRIC CALCULATIONS Calculate the quantity of analyte from titration data Example: A 100.0mL sample of brackish water was made ammoniacal, and the sulfide it contained was titrated with 16.47mL of M AgNO 3. The analytical reaction is 2Ag + + S 2- Ag 2 S (s) Calculate the concentration of H 2 S in the water in ppm. (Ag: g/mol, S: g/mol) Ans: H 2 S = 64.8ppm

25 Editor: Wan Norfazilah Wan Ismail Author: Siti Maznah Kabeb Industrial Chemistry Programme Faculty of Industrial Sciences & Technology Universiti Malaysia Pahang

Chapter 13. Titrations in Analytical Chemistry

Chapter 13. Titrations in Analytical Chemistry Chapter 13 Titrations in Analytical Chemistry Titrations in Analytical Chemistry Titration methods are based on determining the quantity of a reagent of known concentration that is required to react completely